A transposon-based transfection system for primary cells

ABSTRACT

The present invention relates to the field of genetic engineering, in particular, to a transposon-based transfection kit suitable for transfection of primary cells, such as T cells, comprising mRNA encoding a transposase, or reagents for generating mRNA encoding said transposase, as well as minicircle DNA comprising the transposon. The invention also relates to a nucleic acid, preferably, a DNA minicircle, comprising a transposon, wherein the transposon encodes a protein and at least one miRNA, wherein the sequences encoding the miRNA are located in an intron and expression of the protein and the miRNA is regulated by the same promoter. The invention also provides a population of cells obtainable with the method of the invention. Methods of transfection are also provided, as well as medical use, e.g. in immunotherapy, in particular, in adoptive T cell therapy or T cell receptor (TCR) or chimeric antigen receptor (CAR) gene therapy.

The present invention relates to the field of genetic engineering, in particular, to a transposon-based transfection kit suitable for transfection of cell lines and primary cells, such as T cells, comprising mRNA encoding a transposase, or reagents for generating mRNA encoding said transposase, as well as minicircle DNA comprising the transposon. The invention also relates to a nucleic acid, preferably, a DNA minicircle, comprising a transposon, wherein the transposon encodes at least one protein and at least one miRNA, wherein the sequences encoding the miRNA are located in an intron and expression of the protein and the miRNA is regulated by the same promoter. The invention also provides a population of cells obtainable with the method of the invention. Methods of transfection are also provided, as well as medical use, e.g. in immunotherapy, in particular, in adoptive T cell therapy using T cell receptor (TCR) gene-modified T cells (TCR gene therapy) or chimeric antigen receptor (CAR) gene-modified T cells (CAR gene therapy).

Adoptive T cell therapy (ATT) is a promising immunotherapeutic strategy to treat cancer, chronic infections, and autoimmune diseases. ATT requires the preparation of large numbers of antigen-specific T cells that recognize and eradicate diseased cells. ATT involves on one hand the isolation, expansion, and reinfusion of naturally occurring, antigen-specific T cells into the patient to treat the disease. However with regard to cancer, most patients lack suitable amounts of naturally occurring antigen-specific T cells (tumor infiltrating lymphocytes, TILs) and moreover, these cells are difficult to isolate from many tumor entities. Therefore, ATT uses on the other hand host cells, which have been engineered with antigen receptor genes (TCR, CAR) to endow the cells with a new antigen specificity. ATT using CAR- and TCR-engineered T cells has been successfully employed to treat cancer and virus-associated diseases, refractory to other treatments (Vonderheide et al., 2014; Robbins et al., 2015).

TCR and CAR gene therapy necessitates the genetic engineering of large numbers of primary human T cells. This can be efficiently done using viral vector systems. However, the technology is laborious, time consuming, and costly. In contrast, the use of plasmid DNA-based transposon vector systems offers several advantages. The production of GMP grade vector (especially large-scale vector production) is faster, less labor-intensive, cost-saving and involves less bureaucratic burden. In addition, the transgene capacity of transposon vectors is larger in comparison to viral vectors and some transposons show a random integration pattern without preference for active genes.

A major drawback using conventional transposon vector systems consisting of two DNA plasmids (FIG. 1A) for the genetic modification of primary cells is the high cell mortality induced by transfection of DNA (FIG. 2A), which hampers rapid expansion of the transfected cells and needs fundamental optimization. Despite of this drawback, transposon-based methods have been successfully applied for the genetic engineering of primary cells, e.g., T cells. However, the conventional method is inefficient because most of the T cells die after transfection and only a small percentage of the surviving cells stably express the transgene. Two strategies were applied to obtain the required number of genetically modified T cells for therapy after the cells were transfected using the conventional method. First, the cells were selectively expanded with the help of a stimulator cell line presenting the specific ligand of the transferred antigen receptor (Singh et al., 2013). As a result, the generation of a new stimulator cell line for every antigen receptor with a new specificity is required. Furthermore, such selective outgrowth of the modified cells cannot be induced in situations where the specificity of the transferred antigen receptor is unknown or the transposon does not encode an antigen receptor. The second strategy is that the transfected cells were sorted for surface expression of the transferred TCR with the help of a specific antibody. Afterwards, the sorted cells were expanded using allostimulation (Deninger et al., 2016). This strategy requires the transfection of a TCR with full-length mouse constant regions, which are immunogenic in humans, and an antibody that is approved for clinical protocols. Furthermore, the sorted T cells are stimulated through their endogenous TCR in this protocol. Cells in which the transferred TCR completely replaced the endogenous TCR cannot be expanded this way. Therefore, allogeneic stimulation is inherently incompatible with the intent to generate cells for therapy that express as much as possible transferred TCR on their surface. Finally, neither selective expansion nor sorting of transfected cells directly addresses the issues of low transfection rates and high cell mortality. In conclusion, there is a considerable need to provide more efficient methods and kits for the genetic engineering of such cells, in particular of primary cells and other cells which are hard to transfect with reasonable efficacy.

This problem is solved by the present invention, in particular, by the subject matter of the claims.

The present invention provides a kit comprising

-   a) a nucleic acid encoding a transposase capable of mobilizing a     transposon, wherein the nucleic acid is selected from the group     comprising     -   (i) mRNA encoding said transposase; or     -   (ii) DNA encoding said transposase functionally linked to a         promoter, wherein the kit optionally further comprises reagents         suitable for in vitro transcription comprising ribonucleotide         triphosphates, a buffer suitable for transcription, and a RNA         polymerase suitable for transcription; and -   b) minicircle DNA comprising said transposon, wherein the transposon     encodes a protein and/or a miRNA, wherein expression of the protein     and/or the miRNA is regulated by a promoter.

In the context of the present invention “a” does not exclusively refer to “one”, but also encompasses “two or more”. Accordingly, the transposon may encode one or more proteins and/or one or more miRNA. For example, the transposon may encode two proteins and one miRNA. Preferably, it encodes one protein and two (or more) miRNAs. Of course, it may also encode two proteins and two miRNAs.

In one embodiment, the nucleic acid of a) is mRNA which has been transcribed in vitro, i.e., ivtRNA (FIG. 1B). Purified RNA may also be used. RNA should be of high quality and high concentration, e.g., comparable to ivtRNA routinely obtained. Quality is determined (a) by the amount of mRNAs formed with a 5′ cap analog, (b) the poly(A) tail and (c) purity of the RNA.

The inventors could show that use of the kit of the invention comprising ivtRNA encoding the transposase led to both high transfection efficiency, compared to DNA encoding transposase (FIG. 3) and improved viability (FIG. 4) of human T cells.

In an alternative embodiment, the nucleic acid encoding the transposase is DNA suitable for in vitro transcription. Preferably, in that embodiment, the kit also comprises reagents and, optionally, instructions, for in vitro transcription, such as ribonucleotide triphosphates containing 5′ cap analogs, a buffer suitable for transcription, and an RNA polymerase suitable for in vitro transcription, e.g., T7 RNA polymerase. The DNA may be a vector for RNA production, e.g., pcDNA3.1+(hygro) (Thermo Fisher Scientific, Waltham, USA). The kit may comprise rabbit reticulocyte lysate, which comprises all reagents for in vitro transcription. Such a kit is to be used for producing ivtRNA, which is then, in accordance with the invention, used for preparing transfected cells, in particular transfected primary cells, preferably, primary T cells, or stem cells. Such cells are known to be especially hard to transfect.

The transposase encoded by the nucleic acid may be a transposase functional in vertebrate cells, in particular, in human cells. It is selected from the group of class II transposable elements comprising Sleeping Beauty transposase, FrogPrince, piggyBac, Tol2 and other Tc1/mariner-type transposases, preferably, Sleeping Beauty transposase, e.g., as disclosed in Ivies et al., 1997, most preferably, SB100X (Mátés et al., 2009).

The kit of the invention, as a second nucleic acid, further comprises minicircle DNA comprising the transposon, which can be mobilized by the transposase (FIG. 1C). In the context of the invention, the transposon does not encode a transposase itself The transposon encodes a protein and/or a miRNA, wherein expression of the protein and/or the miRNA is regulated by a promoter. Minicircles are small circular plasmid derivatives that have been largely or completely freed from non-essential prokaryotic vector parts. In particular, minicircles do not contain DNA encoding for bacterial sequences like antibiotic resistance genes or the ORI.

The minicircle DNA of the invention preferably comprises less than 5 kb, more preferably, less than 4 kb, less than 3 kb or less than 2 kb. The inventors found that a minimal size of the DNA minicircle improves efficiency. The minicircle encodes an expression cassette comprising a promoter, an intron and a poly(A) signal as well as the TIR (terminal inverted repeats) of the transposon and a spacer, which altogether comprise about 1.75 kb. The final size of the minicircle depends on the size of the coding region.

Minicircles and their use in combination with Sleeping Beauty transposase are described in DE 10 2011 118 018 A1 or Garrels et al., 2016.

The inventors could show that use of the kit of the invention comprising mRNA encoding the transposase in combination with minicircle DNA comprising the transposon led to surprisingly both high transfection efficiency and cell viability (FIG. 5). This is of particular importance for the transfection of delicate or hard-to-transfect cells such as T cells, B cells, stem cells, and many other cell types, in particular, primary cells (FIG. 12).

The invention thus also provides a method for producing transfected cells, in particular transfected primary cells or stem cells, preferably, primary T cells such as primary human T cells, with high transfection efficiency and high viability. High or improved viability preferably is higher than 30%, more preferably, higher than 35% or higher than 40%. Viability may, e.g., be assessed on day 4 after transfection. High transfection efficiency preferably is higher than 50%, or more preferably, higher than 60% of viable cells. Said method comprises use of the kit of the invention. In particular, it comprises steps wherein the cells are contacted with

-   -   a) mRNA encoding a transposase capable of mobilizing a         transposon, preferably, Sleeping Beauty,     -   b) minicircle DNA comprising said transposon, wherein the         transposon encodes at least one protein and/or at least one         miRNA, wherein expression of the protein and/or the miRNA is         regulated by a promoter. Preferably, the transposon encodes a         protein and at least one, preferably, two miRNA, wherein         expression of the protein and the miRNA is regulated by the same         promoter.

Preferably, said contacting comprises electroporation.

In a preferred embodiment of the invention, the transposon encodes a protein and a miRNA (FIG. 1D). Preferably, the transposon encoding a protein comprises an intron comprising sequences encoding the miRNA, wherein the expression of the protein and the miRNA is regulated by the same promoter (FIG. 6A). In a preferred embodiment, the transposon encoding a protein comprises an intron comprising sequences encoding at least two miRNAs, wherein the expression of the protein and the miRNAs is regulated by the same promoter.

The invention thus also provides a nucleic acid comprising a transposon, wherein the transposon encodes at least one protein and at least one miRNA, wherein the nucleic acid encoding the protein comprises an intron comprising sequences encoding the miRNA, wherein expression of the protein and the miRNA is regulated by the same promoter. The nucleic acid is selected from the group comprising a plasmid or minicircle DNA, preferably, a minicircle DNA. If the nucleic acid is not a minicircle DNA, it is suitable for generation of a minicircle DNA, as it comprises recombination sites outside the integration cassette which allow the production of a minicircle vector during propagation in a specific bacteria strain suitable for production of minicircles (Kay et al., 2010), e.g., ZYCY10P3S2T. (System Biosciences, Mountain View, USA). Such strains, e.g., are capable of expressing PhiC31 integrase and I-SceI endonucleoase. Said nucleic acid can, e.g., be an intermediate product in production of the kit of the invention.

A preferred intron employed in the transposon of the invention is a chimeric intron comprising a 5′-splice donor site from a first intron of a human β-globin gene and a 3′-splice acceptor site from an immunoglobulin gene heavy chain variable region, e.g., as disclosed in US20070190617. Preferable features of the intron are described in the data sheet for pCI and pSI mammalian expression vectors, Promega 7/09, and preferably, the intron comprised in said vectors is employed. Choi et al., 2014, Mol Brain 7:17 references the sequence of a vector comprising said intron.

In the state of the art, miRNAs are normally expressed from a different promoter, or placed 3′ or 5′ of the transgene. The incorporation of miRNA in introns has been shown to improve transgene expression (Chung et al., 2006). Notably, viral vectors do not allow the application of efficient introns. With the transposon of the invention, the inventors were able to silence several cellular factors of the target cells by incorporating multiple miRNAs and to gain high transgene expression levels at the same time. A similar gene silencing approach incorporated into gamma-retroviral vectors would result in decreased transgene expression levels.

An additional advantage of transposons versus viral vectors is that, according to the invention, in the context of transposons, two or more miRNA comprising the same miRNA backbone, and, e.g., even having the same complete miRNA sequence, can be used without compromising stability. This increases efficiency of downregulation of the target without requiring optimization of sequences (FIG. 8). In contrast, Amendola at al., 2009, showed that using the same miRNA twice in a viral vector led to instability and rearrangement of said vector. Thus, in a viral system, it is necessary to find a compromise between optimal efficiency of miRNAs, which depends on the interaction between miRNA backbone and target sequences, and the necessity to prevent recombination between identical or similar miRNA. In contrast, in the transposon system according to the invention, it is not necessary to find such compromises.

The invention further provides a nucleic acid comprising a transposon, wherein the transposon encodes at least one protein and two or more miRNA, preferably, three or more miRNA, four or more miRNA, five or more miRNA or six or more miRNA, wherein the nucleic acid encoding the protein comprises an intron comprising sequences encoding the miRNA, wherein expression of the protein and the miRNA is regulated by the same promoter. Optionally, of said miRNA, two or more miRNA, preferably, three or more miRNA, four or more miRNA, five or more miRNA or six or more miRNA, e.g, all miRNA, comprise the same backbone.

Preferably, for use in ATT, the protein encoded by the transposon is a TCR or CAR construct. The TCR construct may comprise one TCR alpha chain construct and one TCR beta chain construct, or a single chain TCR construct or a CAR construct. Preferably, the TCR construct comprises a TCR alpha chain construct and a TCR beta chain construct. Preferably, the CAR construct comprises a single chain variable fragment of an antibody (scFv) construct, a spacer region construct and a signaling region construct.

Optionally, codon usage of the TCR alpha chain construct and a TCR beta chain construct may be optimized to enhance expression of the TCR in recombinant T cells. Human variable regions may be combined with murine constant regions (Cohen et al., 2006), or a minimal murine constant region, i.e., human constant regions containing only defined amino acids from the murine constant region (Sommermeyer et al., 2010; Bialer et al., 2010) and additionally comprising an additional cysteine bridge (Cohen et al., 2007; Kuball et al., 2007), which increases preferential binding of transgenic TCR chains to each other and reduces pairing with endogenous TCR chains expressed by recipient T cells. The inventors have demonstrated that, optimally, the TCR construct comprises a TCR alpha chain and a TCR beta chain optimized for pairing with each other, wherein the TCR alpha and beta chain constructs preferably each comprise (a) additional Cys residues relative to native human TCRs and (b) murine amino acid sequences in the constant regions, wherein otherwise, the TCR chains are of human origin. In a preferred embodiment, the TCR construct comprises SEQ ID NO: 23.

Single chain (sc) TCR constructs are encompassed as well as heterodimeric TCR constructs. A scTCR can comprise a variable region of a first TCR chain construct (e.g., an alpha chain) and an entire (full-length) second TCR chain (e.g., a beta chain), or vice versa. Furthermore, the scTCR can optionally comprise one or more linkers, which join the two or more polypeptides together. The linker can be, for instance, a peptide, which joins together two single chains. A scTCR which is fused to a cytokine, e.g., a human cytokine, such as IL-2, IL-7, IL-15 or IL-21, can also be encoded.

Furthermore, soluble receptor molecules and fusion proteins may be generated containing the variable regions of the TCR alpha and TCR beta chain genes and e.g. antibody domains. These can be Ig domains, e.g., an IgG constant domain. Also, variable regions of the TCR chains may be fused to, e.g., anti-CD3 antibody domains in a fusion protein of the invention, e.g., to provide soluble monoclonal TCR reagents to target malignant cells expressing the respective peptide-major histocompatibility complex (pMHC) at the cell surface and engaging T cells via e.g. an anti-CD3 targeting domain to provide effector functions to the target cells (Liddy et al., 2012).

The TCR construct is capable of specifically binding to an antigen, preferably, an antigen specifically expressed or overexpressed by cancer cells and/or cells infected by a virus as well as cells involved in autoimmune diseases. The term “capable of specifically binding” or “recognizing” or “specific for” a given antigen, as used herein, means that a TCR construct can specifically bind to and immunologically recognize an epitope, preferably with high affinity and through its variable domains. Affinity can be analyzed by methods well known to the skilled person, e.g. by BiaCore.

In a preferred embodiment, the transposon further encodes at least two miRNAs, optionally, three, four, five, six, seven, eight, nine, ten or more miRNAs (FIG. 6A, B). In combination with the encoded protein being a TCR construct or CAR construct, it is preferred that the miRNA encoded by the transposon is capable of suppressing the expression of a TCR alpha and/or TCR beta chain, in particular, both endogenous TCR chains of the T cell. Mispairing of TCR chains is thus prevented. Expression of the encoded protein, however, is not silenced, in particular, the miRNA is not capable of silencing expression of the TCR chain or TCR construct or CAR encoded by the transposon. Preferably, the TCR chain or TCR construct encoded by the transposon is codon-optimized and the sequence thus differs significantly from the endogenous TCR sequences. Embodiments wherein the miRNA encoded by the transposon is capable of suppressing the expression of a TCR alpha and/or TCR beta chain, in particular, both endogenous TCR chains of the T cell can also be of interest, e.g., for prevention of GvHD (graft-versus-host disease) or reduction of GvHD (cf. U.S. Pat. No. 9,181,527).

The inventors were able to show that the minicircle DNA transposon constructs of the invention are suitable for co-expression of a transgene and even multiple miRNAs, without abrogating the expression of the transgene. Suppression of endogenous TCR expression reduces generation of potentially dangerous mixed TCRs that are composed of one endogenous and one transgenic TCR chain. Also, silencing of the endogenous TCR (FIG. 6C) facilitates expression of the transgenic, therapeutic TCR that requires cellular co-factors for surface expression. Thus, the transposon-based vector of the invention provides for both an efficient expression of functional TCR (FIG. 6D, FIG. 7A, B) and a crucial safety feature.

The transposon preferably encodes two miRNAs capable of silencing expression of a TCR alpha chain and TCR beta chain. The miRNAs are typically capable of silencing the expression of the endogenous TCR chains of the T cell, which is to be genetically modified. Suitable exemplary sequences encoding miRNAs are provided in SEQ ID NO: 15 and SEQ ID NO: 16, or in SEQ ID NO: 19.

In one embodiment, the transposon encodes two or more, preferably, two miRNA having the same backbone sequences, or two or more miRNA having the same sequence.

Alternatively or additionally, a miRNA encoded by the transposon is capable of silencing expression of a protein capable of limiting the therapeutic efficiency of the transferred cells. In case of immunotherapy of cancer or virus-associated disease the protein capable of downregulating effector functions and/or proliferation of a T cell is selected from the group of inhibitory surface receptors comprising CTLA4, PDCD1, LAG3, HAVCR2 and TIGIT, from the group of intracellular proteins that negatively regulate TCR or costimulatory pathways comprising CBLB, CISH, DGK and TNFAIP3, from the group of intracellular proteins that limit cytokine production comprising SPRY2 and CREM or from the group of proteins stabilizing a dysfunctional T cell phenotype comprising MAF, EGR3, NDRG1 and DTX1.

In the context of ATT, the promoter, which regulates expression of the protein and/or the miRNA(s) is functional for expression in a T cell. Preferably, MPSV promoter may be used for T cell engineering. Alternative promoters are EF1a, PGK, CMV, CAG and others.

In one embodiment, the invention provides pSB-miR-T1367 (SEQ ID NO: 22), or the parental plasmid for generation of a minicircle of the invention according to SEQ ID NO:14. Of course, the plasmid or minicircle may alternatively encode a different TCR construct.

In a preferred embodiment, throughout the invention, the transposon comprises a cargo nucleic acid flanked by a left and a right inverted repeat/direct repeat (IR/DR), wherein

-   -   (i) the transposon is capable of being mobilized by a Sleeping         Beauty transposase protein;     -   (ii) the left IR/DR comprises an outer left DR motif and an         inner left DR motif, wherein the outer left DR motif comprises         the nucleotide sequence of SEQ ID NO:1 and the inner left DR         motif comprises the nucleotide sequence of SEQ ID NO: 2; and     -   (iii) the right IR/DR comprises an outer right DR motif and an         inner right DR motif, wherein the outer right DR motif comprises         an inverted sequence of the nucleotide sequence of SEQ ID NO:1         and the inner right DR motif comprises an inverted sequence of         the nucleotide sequence of SEQ ID NO: 2.

The cargo nucleic acid comprises the at least one protein and at least one miRNA of the invention. Preferably, said outer left DR motif comprises the nucleotide sequence of SEQ ID NO:3 and/or said outer right DR motif comprises an inverted sequence of the nucleotide sequence of SEQ ID NO:4. Preferably, the inner left DR motif comprises the nucleotide sequence of SEQ ID NO: 5 and/or the inner right DR motif comprises an inverted sequence of the nucleotide sequence of SEQ ID NO: 6. Preferably, the left IR/DR comprises a HDR region capable of functioning as an enhancer comprising the nucleotide sequence of SEQ ID NO:7 between the outer DR and inner DR, wherein, optionally, the right IR/DR also comprises reverse complement of said HDR region. Preferably, the left IR/DR comprises the nucleotide sequence selected from the group consisting of SEQ ID NO: 8 and SEQ ID NO: 9. Preferably, the right IR/DR comprises the reverse complement nucleotide sequence selected from the group consisting of SEQ ID NO: 10, SEQ ID NO:11, SEQ ID NO: 12 and SEQ ID NO: 13. It was shown that such transposons, designated pT4 or pT5 transposons, have high efficiencies of transposition, and can thus be advantageously used in the context of the present invention.

TABLE 1 Preferred IR/DR sequences Left IR/DR of pT4 with HDR: Left outer DR SEQ ID NO: 1 CAGTTGAAGT CGGAAGTTTA CATACACYTW AG Left inner DR SEQ ID NO: 2 YCCAGTGGGT CAGAAGT G TA CATACAC G V K   C T HDR SEQ ID NO: 7 GTKTA CAKACASD Framework: pT SEQ ID NO: 8 TACAGTTGAAGTCGGAAGTTTACATACACYTWAGTTGGAGTCATTAAAACTCGTTTTTCAACTACTCCACAAATTTC TTGTTAACAAACAATAGTTTTGGCAAGTCAGTTAGGACATCTACTTTGTGCATGACACAAGTCATTTTTCCAACAAT TGTKTACAKACASDTTATTTCACTTATAATTCACTGTATCACAATYCCAGTGGGTCAGAAGTGTACATACACGVKCT Left IR/DR of pT5 with HDR: Left outer DR SEQ ID NO: 1 CAGTTGAAGT CGGAAGTTTA CATACACYTW AG Left inner DR SEQ ID NO: 2 YCCAGTGGGT CAGAAGT G TA CATACAC G V K   C T HDR SEQ ID NO: 7 GTKTA CAKACASD Framework: pT2 SEQ ID NO: 9 TATACAGTTGAAGTCGGAAGTTTACATACACYTWAGTTGGAGTCATTAAAACTCGTTTTTCAACTACTCCACAAATT TCTTGTTAACAAACAATAGTTTTGGCAAGTCAGTTAGGACATCTACTTTGTGCATGACACAAGTCATTTTTCCAACA ATTGTKTACAKACASDTTATTTCACTTATAATTCACTGTATCACAATYCCAGTGGGTCAGAAGTGTACATACACGVK CT Right IR/DR of pT4 without HDR (right IR/DR comprises the reverse complement of the given sequences): Right outer DR SEQ ID NO: 1 CAGTTGAAGT CGGAAGTTTA CATACACYTW AG Right inner DR SEQ ID NO: 2 YCCAGTGGGT CAGAAGT G TA CATACAC G V K   C T Framework: pT SEQ ID NO: 10 TACAGTTGAAGTCGGAAGTTTACATACACYTWAGCCAAATACATTTAAACTCACTTTTTCACAATTCCTGACATTTA ATCCGAGTAAAGATTCCCTGTCTTAAGGTCAGTTAGGATCACCACTTTATTTTAAGAATGTGAAATATCAGAATAAT AGTAGAGAGAATGATTCATTTCAGCTTTTATTTCTTTCATCACATTYCCAGTGGGTCAGAAGTGTACATACACGVKC T Right IR/DR of pT5 without HDR (right IR/DR comprises the reverse complement  of the given sequences): Right outer DR SEQ ID NO: 1 CAGTTGAAGT CGGAAGTTTA CATACACYTW AG Right inner DR SEQ ID NO: 2 YCCAGTGGGT CAGAAGT G TA CATACAC G V K   C T Framework: pT2 SEQ ID NO: 11 TATACAGTTGAAGTCGGAAGTTTACATACACYTWAGCCAAATACATTTAAACTCACTTTTTCACAATTCCTGACATT TAATCCTAGTAAAAATTCCCTGTCTTAGGTCAGTTAGGATCACCACTTTATTTTAAGAATGTGAAATATCAGAATAA TAGTAGAGAGAATGATTCATTTCAGCTTTTATTTCTTTCATCACATTYCCAGTGGGTCAGAAGTGTACATACACGVK CT Right IR/DR of pT4 with HDR (right IR/DR comprises the reverse complement of the given sequences): Right outer DR SEQ ID NO: 1 CAGTTGAAGT CGGAAGTTTA CATACACYTW AG Roght inner DR SEQ ID NO: 2 YCCAGTGGGT CAGAAGT G TA CATACAC G V K   C T HDR SEQ ID NO: 7 GTKTA CAKACASD Framework: pT SEQ ID NO: 12 TACAGTTGAAGTCGGAAGTTTACATACACYTWAGCCAAATACATTTAAACTCACTTTTTCACAATTCCTGACATTTA ATCCGAGTAAAGATTCCCTGTCTTAAGGTCAGTTAGGATCACCACTTTATTTTAAGAATGTGAAATATCAGAATAAT AGTAGAGAGAATGATGTKTACAKACASDTCATTTCAGCTTTTATTTCTTTCATCACATTYCCAGTGGGTCAGAAGT GTACATACACGVKCT Right IR/DR of pT5 with HDR (right IR/DR comprises the reverse complement of the given sequences): Right outer DR SEQ ID NO: 1 CAGTTGAAGT CGGAAGTTTA CATACACYTW AG Right inner DR SEQ ID NO: 2 YCCAGTGGGT CAGAAGT G TA CATACAC G V K   C T HDR SEQ ID NO: 7 GTKTA CAKACASD Framework: pT2 SEQ ID NO: 13 TATACAGTTGAAGTCGGAAGTTTACATACACYTWAGCCAAATACATTTAAACTCACTTTTTCACAATTCCTGACATT TAATCCTAGTAAAAATTCCCTGTCTTAGGTCAGTTAGGATCACCACTTTATTTTAAGAATGTGAAATATCAGAATAA TAGTAGAGAGAATGATGTKTACAKACASDTCATTTCAGCTTTTATTTCTTTCATCACATTYCCAGTGGGTCAGAAG TGTACATACACGVKCT Y = C/T, wherein Y preferably is T in the left DRs and C in the right DRs; W = A/T, wherein W preferablyis A in the left DRs and T in the right DRs; V = A/G/C, wherein V preferably is C; K = G/T, wherein K preferably is G; S = C/G, D = A/T/G. Most preferably, Y is T in the left DRs and C in the right DRs; W is A in the left DRs and T in the right DRs; V is C; S is C, D is G and K is G.

In a preferred embodiment of the transposon, the left IR/DR comprises the nucleotide sequence of SEQ ID NO: 8 and the right IR/DR comprises the reverse complement nucleotide sequence of SEQ ID NO: 10 or SEQ ID NO:12. In these polynucleotides, the framework region corresponds to pT, and the polynucleotide of the invention is designated pT4.

In another preferred embodiment of the transposon, the left IR/DR comprises the nucleotide sequence of SEQ ID NO: 9 and the right IR/DR comprises the reverse complement nucleotide sequence of SEQ ID NO: 11 or SEQ ID NO:13. In these polynucleotides, the framework region corresponds to pT2, and the polynucleotide of the invention is designated pT5.

The minicircle DNA comprising the transposon, e.g., as described above and in the examples, is preferably comprised in the kit of the present invention.

The present invention also comprises a method for preparing transfected cells, wherein the cells which are transfected preferably are primary cells, most preferably primary T cells, the method comprising transfecting cells with the nucleic acids of the kit of the invention, the nucleic acids comprising a) mRNA encoding a transposase capable of mobilizing a transposon; and b) minicircle DNA comprising said transposon, wherein the transposon encodes a protein and/or a miRNA, wherein expression of the protein and/or the miRNA is regulated by one promoter.

Preferably, the cells are transfected by electroporation, however, other non-viral transfection methods are also possible, e.g., physical methods such as cell squeezing, sonoporation, hydrodynamic delivery, chemical-based transfection methods with calcium phosphate, dendrimers, liposomes or cationic polymers, or particle-based methods such as with a gene gun.

In the method of the invention, preferably, the cells, which are transfected, e.g., electroporated, are primary human T cells isolated from a patient. In that case, the method optionally further comprises stimulating the T cells with one or more stimulants selected from the group comprising anti-CD3 antibodies, anti-CD28 antibodies, anti-CD137 antibodies, anti-CD134 antibodies, anti-CD357 antibodies, IL-2, IL-7, IL-15, and IL-21. However, the inventors could show that, in the method of the invention, even without such a stimulus, the transfected T cells survive and can be expanded.

In one embodiment, the method of the invention does not comprise selection and/or enrichment of the transfected cells.

The method of the invention thus also constitutes a method for preparing transfected cells having an enhanced viability. Using a preferred transposon of the invention encoding a TCR construct and miRNAs capable of downregulating expression of endogenous TCR chains, the method of the invention is particularly suitable for preparing transfected TCR transgenic cells having a reduced expression of endogenous TCR chains, and/or for reducing pairing of transgenic and endogenous TCR chains.

Using the kit and method of the invention, T cells specific for an epitope from a defined antigen presented on a major histocompatibility complex (MHC) may be generated by expressing the nucleic acids encoding the TCR construct. If such T cells are intended for therapy of a patient, it is preferred to use autologous T cells. Alternatively, an allogeneic setting is possible, using immune suppression.

The invention also provides a population of genetically modified cells, e.g., T cells, comprising the transposon described above or in the examples which encodes at least one protein and at least one miRNA, wherein the nucleic acid encoding the protein comprises an intron comprising sequences encoding the miRNA, wherein expression of the protein and the miRNA is regulated by the same promoter. Said population of genetically modified cells is preferably obtainable by the method of the invention.

The invention also provides a pharmaceutical composition comprising a population of genetically modified cells as described above, e.g., comprising the transposon described above or in the examples which encodes at least one protein and at least one miRNA, wherein the nucleic acid encoding the protein comprises an intron comprising sequences encoding the miRNA, wherein expression of the protein and the miRNA is regulated by the same promoter. Preferably, said pharmaceutical composition is for use in treating a patient by adoptive T cell therapy, wherein the patient is selected from the group comprising cancer patients and/or patients infected with a viral or bacterial pathogen and/or patients with autoimmune diseases, and wherein the cells comprise T cells expressing a TCR or CAR construct, and, preferably, miRNA suppressing expression of the T cells endogenous TCR. The pharmaceutical composition may be for use in prevention of infection or in reducing infection with a pathogen such as a virus, e.g., CMV, EBV, HIV or HPV, wherein suitable TCR or CAR constructs are employed.

The invention also teaches a method of treatment of a patient in need thereof (e.g., infected with a virus, or suffering from cancer, e.g., cancer associated with a virus, e.g., suffering from an autoimmune disease), or of reducing infection with a virus, or symptoms of said infection, comprising administering to said patient a suitable pharmaceutical composition of the invention.

Throughout the invention, the T cells may be CD8⁺ or CD4⁺ T cells, preferably CD8⁺ cells or regulatory T cells. Pharmaceutical compositions may also comprise both transgenic CD4⁺ and CD8⁺ T cells, wherein the respective TCRs are preferably directed to different epitopes of the same antigen. Preferably, the T cells are human T cells, and the patient to be treated is a human patient.

The invention is further illustrated by the examples below, which are intended to exemplify the invention, and not to limit its scope. All references cited herein are herewith fully incorporated. All embodiments of the invention disclosed herein can be combined.

FIGURES

FIG. 1

Schematic overview of improvements of the Sleeping Beauty transposon-based gene transfer system applied in the invention.

In comparison to the conventional Sleeping Beauty transfer system (A) the kit of the invention includes a mRNA (ivtRNA) encoding the Sleeping Beauty transposase (B), minicircle DNA comprising the transposon encoding the transgene (C) and miRNAs silencing endogenous genes, which hamper efficient transgene, e.g. TCR, expression and therapeutic efficacy (D).

FIG. 2

Transfection of plasmid DNA into human T cells leads to dose-dependent T cell mortality.

Human T cells transfected with GFP-encoding plasmid DNA (pSB-GFP) revealed a dose-dependent mortality while similar amounts of transfected GFP-mRNA showed only a slight reduction in T cell counts (A). Transfection of GFP-ivtRNA is more efficient and results in more GFP⁺ T cells compared to transfection of pSB-GFP. Furthermore, the transfection of high DNA amounts (>10 μg) results in a decrease of GFP⁺ T cells three to four days after transfection (B).

FIG. 3

Transposase delivered as ivtRNA and as transposase encoding plasmids yield similar gene transfer efficiency.

Comparison of GFP expression in human T cells using the conventional Sleeping Beauty transposon-based gene transfer system delivering the transposase as DNA plasmid (SBTS-co) and the Sleeping Beauty transposon-based gene transfer system of the invention delivering the transposase as ivtRNA (SBTS-iR). Shown is the percentage of GFP⁺CD3⁺ T cells at day 1 (transient expression) and day 12 (stable expression).

FIG. 4

Sleeping Beauty transposon-based gene transfer delivering the transposase as ivtRNA increases cell viability.

SBTS-co and SBTS-iR, as sown in FIG. 2, are employed to transfect human T cells with a GFP-encoding transposon. Shown is the percentage of viable T cells 24 hrs after transfection using different amounts of transposon plasmid and either DNA transposase or ivtRNA transposase.

FIG. 5

Sleeping Beauty transposon-based gene transfer using a minicircle DNA transposon increases transfection efficiency.

Comparison of Sleeping Beauty transposon-based gene transfer system containing transposase encoding ivtRNA and either transposon plasmid DNA (pSB) or transposon minicircle DNA (mSB), both encoding GFP (A). Shown are the Mean Fluorescence Intensity, MFI (B) and the percentage of GFP⁺ human T cells (C). pmax-GFP represents a transient transfection control without ivtRNA transposase, non-TF represents transfection conditions without employing nucleic acids.

FIG. 6

Sleeping Beauty transposon-based gene transfer system delivering a minicircle transposon DNA encoding an engineered TCR and miRNA for endogenous TCR silencing results in improved expression of the therapeutic TCR.

Minicircle transposon vector harboring miRNAs (miR) and modifications in the MAGE-A1-reactive TCR T1367 sequence (A). Minicircle transposon vectors containing the TCR T1367 with different modifications. 1: TCR codon-optimized; 2: as 1 plus miRNA cassette (miR); 3 TCR codon-optimized, additional cysteine bond, minimal murinized C-regions (opt); 4 as 3 plus miRNA cassette (miR opt) (B). Expression of miRNA decreases the formation of mispaired TCRs formed between therapeutic and endogenous TCR chains (C). Expression of miRNA increases the functionality of TCR-engineered human T cells as measured by MHC multimer binding (D).

FIG. 7

Human T cells engineered with a fully optimized Sleeping Beauty transposon-based gene transfer system show improved functionality.

Human T cells were transfected with the fully optimized Sleeping Beauty transposon-based gene transfer system (ivtRNA encoding the transposase, minicircle transposon DNA containing a miRNA to knockdown the expression of endogenous TCRs, optimized therapeutic TCR) and show improved IFN-γ release in response to peptide-loaded indicator cells (A) and a MAGE-Al⁺HLA-A*02:01⁺ (MAGE-A1⁺, A2⁺) tumor cell line while A2⁻ and MAGE-A1⁻ cell lines are not recognized (B).

FIG. 8

Combination of identical miRNAs in one vector (2× same miRNA) is possible with the system of the invention.

Jurkat cells were electroporated with transposase plasmid and SB transposon plasmids encoding for GFP and one (B) or two identical (C) miRNAs specific for the human TCR alpha chain (TRAC, SEQ ID NO: 15) or without miRNA (A) and analyzed by flow cytometry for CD3 surface expression after 8 days. Knockdown rates were 74% with one miRNA cassette and 84% with the same miRNA cassette incorporated twice into the transposon vector.

FIG. 9

Primary human T cells (HTC): plasmid (p) vs. minicircle (mc).

Primary human T cells were electroporated with 15 μg SB transposase RNA and 2.5 μg SB transposon vector as either plasmid or minicircle and analyzed by flow cytometry after 4 days. Providing SB transposons as minicircles instead of conventional plasmids substantially increased transfection efficiency (B) without compromising T cell viability (A).

FIG. 10

Primary human T cells (HTC): SB RNA vs. SB plasmid.

Primary human T cells were electroporated with 2.5 μg SB transposon minicircles encoding for GFP and 15 μg SB transposase as in vitro transcribed RNA (SB RNA) or as plasmid (SB plasmid) and analyzed by flow cytometry after 4 days. Providing SB transposase as RNA instead of plasmid DNA reduces T cell mortality after transfection, i.e., T cell viability is increased (A). It also increased transfection efficiency (B).

FIG. 11

Primary human T cells (HTC): conventional two plasmid (p) system vs. minicircle (mc)/RNA.

Primary human T cells were electroporated either with the conventional SB two plasmid system using 2.5 μg transposon vector and 2.5 μg transposase vector or with 2.5 μg transposon minicircle and 15 μg SB RNA and analyzed by flow cytometry after 4 days. The application of minicircles and RNA instead of the conventional two plasmid system substantially increased transfection efficiency (B) without compromising T cell viability (A).

FIG. 12

Comparison of Jurkat cells and Primary human T cells (HTC): conventional two plasmid (p) system vs. minicircle (mc)/RNA.

Alternative approaches use large amounts of plasmid DNA to achieve similar efficiencies. However, usage of these large amounts of plasmid DNA leads to high cell mortality impeding large scale generation of T cells for clinical application. Whereas this approach works for the transfection of cell lines, primary T cells rarely survive transfection with large amounts of DNA. Furthermore, DNA-transfected primary T cells show a delay in T cell activation and hence are hard to expand. Here, we compare our approach using transposon minicircles and transposase RNA with conventional approaches using large amounts of plasmid DNA. Primary human T cells (A) or Jurkat cell line cells (B) were electroporated with the conventional SB two plasmid system using large amounts of DNA (10 μg/10 μg or 20 μg/10 μg) that have been reported to achieve high transfection efficiency, or with our minicircle/RNA approach and analyzed by flow cytometry after 4 days. Whereas Jurkat cells tolerate large amounts of DNA, primary T cells hardly survive the application of 20 μg or 30 μg of total DNA. Our minicircle/RNA approach, however, enables efficient transfection of primary T cells ensuring viable T cells after electroporation (30-40% viability).

EXAMPLES Example 1

Production of Conventional Sleeping Beauty Gene Transfer System (SBTS-Co)

The Sleeping Beauty pT2/HB transposon plasmid (Cui et al., 2002) was modified to carry the MPSV promoter of the MP71 retroviral vector (Engels et al., 2003), a chimeric intron, and the polyA signal of psiCHECK2 (Promega, Madison, USA). The enhanced green fluorescent protein (GFP) and the MAGE-A1-specific human TCR T1367 transgene (Obenaus et al., 2015), respectively, was then cloned into the modified pT2 vector to obtain pSB-GFP and pSB-T1367, respectively.

For efficient TCR expression, the TCR T1367 sequence was codon-optimized (Geneart, Darmstadt, Germany) and the TCRα- and TCRβ-chain were linked via the 2A element of porcine teschovirus (P2A) by PCR (Leisegang et al., 2008). TCR T1367 human constant regions were replaced by minimally murinized counterparts (Sommermeyer and Uckert, 2010) containing an additional cysteine bridge (Kuball et al., 2007; Rosenberg et al., 2008), (T1367opt). The final TCR construct corresponds to SEQ ID NO: 23 (Patent WO2014118236 A2, High avidity antigen recognizing constructs). Transposon plasmid DNA (pSB-GFP, pSB-T1367) was produced using EndoFree Plasmid Maxi Kit (Qiagen, Hilden, Germany). The transposon plasmids were used in conjunction with the Sleeping Beauty SB100X transposase (Mátés et al., 2009), which was delivered as DNA plasmid, to transfect human T cells by electroporation.

Example 2

Production of the Sleeping Beauty Gene Transfer System Using In Vitro Transcribed (Ivt)RNA Transposase (SBTS-iR)

ivtRNA encoding the Sleeping Beauty SB100X transposase or GFP was prepared from pcDNA3.1/Hygro(+) (Invitrogen, Carlsbad, USA) using mMESSAGE mMACHINE T7 kit (ThermoFischer, Waltham, USA) according to the manufacturer's instruction. A poly(A)-tail was added using Poly(A)-tailing kit (ThermoFischer, Waltham, USA) and RNA was purified on columns with RNeasy Kit (Qiagen). ivtRNA transposase was used in conjunction with the modified Sleeping Beauty pT2/HB transposon plasmids (Example 1) to transfect human T cells by electroporation.

Example 3

Production of Sleeping Beauty Transposon Minicircle DNA

For the generation of parental minicircle vectors the cassette containing the promoter, intron, transgene and polyA signal was inserted into the plasmid pMC.BESPX-MCS2 (System Biosciences, Mountain View, USA) via the BamHI restriction site. A 210 bp spacer was inserted between the minicircle recombination site attB and the left inverted repeat. The final plasmid corresponds to SEQ ID NO: 14. Sleeping Beauty transposon minicircle DNA (mSB-GFP, mSB-T1367) was produced using the MC-Easy Minicircle DNA Production kit (System Biosciences, Palo Alto, USA) and EndoFree Plasmid Mega Kit (Qiagen) according to the manufacturers' instruction. A poly(A)-tail was added using Poly(A)-tailing kit (ThermoFischer) and RNA was purified on columns with RNeasy Kit (Qiagen). Transposon minicircle DNA was used in conjunction with ivtRNA transposase (Example 2) to transfect human T cells by electroporation.

Example 4

Production of Micro (mi)RNA for Silencing of Endogenous TCRs

The human TCR-specific miRNA cassettes were designed as described by us for mouse TCRs (Bunse et al., 2014). The TCRα-specific antisense sequence TGA AAG TTT AGG TTC GTA TCT G (SEQ ID NO: 15) and the TCRβ-specific antisense sequence TCT GAT GGC TCA AAC ACA GCG A (SEQ ID NO: 16) were integrated into the miRNA environments miR-155 (Chung et al., 2006), SEQ ID NO:17 and an artificial miRNA (Sætrom et al., 2006), SEQ ID NO: 18, respectively, obtaining SEQ ID NO: 19.

The miRNAs were then inserted into the intron of the TCR transposon plasmid to obtain pSB-miR-T1367co (SEQ ID NO: 22).

Example 5

Isolation and Electroporation of T Cells and Electroporation of Jurkat Cells

T cells were prepared from freshly isolated PBMC by centrifugation on Biocoll (Biochrom, Berlin, Germany) and subsequent enrichment using EasySep Human T Cell Enrichment Kit (STEMCELL Technologies, Köln, Germany). In case of TCR transfer, Vβ3-positive cells were depleted from the cell fraction by incubation with a PE-labeled anti-Vβ3 antibody (clone Jovi-3, Ancell, Bayport, USA) and subsequent selection with anti-PE beads (STEMCELL Technologies, Vancouver, Canada). Electroporation was performed with Amaxa human T cell Nucleofector Kit (Lonza, Basel, Schweiz) for T cells and with Amaxa Cell Line Nucleofector Kit V for Jurkat cells according to the manufacturer's instruction. 6-10×10⁶ T cells or 5-10×10⁶ Jurkat cells were suspended in 100 μl nucleofection buffer and 1.25 μg to 20 μg transposon vector DNA and transferred into a cuvette. Then, program U-14 was applied for T cells, program X-01 for Jurkat cells, cells were immediately supplied with 2 ml T cell medium (TCM: RPMI 1640, 10% fetal calf serum, 1 mM sodium pyruvate, lx non-essential amino acids) and cultured overnight. One day after electroporation, T cells were resuspended in 2 ml fresh TCM supplemented with 400 U/ml recombinant human interleukin-2 (IL-2, Chiron, Marburg, Germany) and activated by seeding them on 24-well plates coated with anti-CD3 (clone OKT3, 5 μg/ml) and anti-CD28 (clone CD28.2, 1 μg/ml) antibodies. Cells were then expanded for up to 18 days. Three to four days prior to functional analysis the concentration of IL-2 was reduced to 40 U/ml.

Example 6

Analytical Measurements:

Flow Cytometry

T cell surface stainings were performed in 50 μl PBS for 30 min at 4° C. with mAbs directed against CD8 (HIT8α), Vβ3 (Jovi-3, Ancell), CD25 (BC96), CD28 and CD3 (UCHT1). Antibodies were purchased from Biolegend (San Diego, USA), eBioscience, BD or Beckman Coulter. MAGE-A1/HLA-A2 multimer (MBL International, Woburn, USA) staining was performed for 30 min at 4° C. T cell viability was determined by dead cell staining with SYTOX Blue (Life Technologies, Carlsbad, USA) and a FSC/SSC lymphocyte gate. Data were acquired on FACS Cantoll (BD) or MACS Quant (Miltenyi Biotec, Bergisch Gladbach, Germany) and analyzed with FlowJo software (Tree Star, Ashland, USA). The MAGE-A1₂₇₈-specific peptide (KVLEYVIKV, SEQ ID NO: 20) and the irrelevant tyrosinase-specific control peptide Tyr₃₆₉ (YMDGTMSQV, SEQ ID NO: 21) were generated by Biosyntan (Berlin, Germany).

Cytokine Release Assay

For detection of secreted cytokines, TCR-modified T cells were seeded in 96-well round-bottom plates (10⁴ per well) together with either MAGE-A1₂₇₈-loaded T2 cells or tumor cell lines in an effector:target (E:T) ratio of 1:1. Supernatants were harvested after 24 h and either analyzed by ELISA or cytometric bead array (both BD).

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1. A kit comprising a) a nucleic acid encoding a transposase capable of mobilizing a transposon, wherein the nucleic acid is selected from the group comprising (i) mRNA encoding said transposase; or (ii) DNA encoding said transposase functionally linked to a promoter, wherein the kit optionally further comprises reagents suitable for in vitro transcription, comprising ribonucleotide triphosphates, a buffer suitable for transcription, and a RNA polymerase suitable for transcription; and b) minicircle DNA comprising said transposon, wherein the transposon encodes at least one protein and/or at least one miRNA, wherein expression of the protein and/or the miRNA is regulated by a promoter.
 2. The kit of claim 1, wherein the nucleic acid encoding the transposase is mRNA.
 3. The kit of claim 1, wherein the transposase is selected from the group of class II transposable elements comprising piggyBac, Tol2 and Tc1/mariner-type transposons comprising Frog Prince and Sleeping Beauty transposase, preferably, Sleeping Beauty transposase, most preferably, SB100X.
 4. A nucleic acid comprising a transposon, wherein the transposon encodes a protein and a miRNA, wherein the nucleic acid encoding the protein comprises an intron comprising sequences encoding the miRNA, wherein expression of the protein and the miRNA is regulated by the same promoter, wherein the nucleic acid is selected from the group comprising a plasmid or minicircle DNA.
 5. The nucleic acid of claim 4, wherein the nucleic acid is minicircle DNA, preferably, comprising less than 5 kb, more preferably, less than 4 kb, less than 3 kb or less than 2 kb.
 6. The nucleic acid of any of claim 4, wherein the protein is a TCR construct, wherein the TCR construct is selected from the group comprising one TCR alpha chain construct and one TCR beta chain construct; and a single chain TCR construct or a chimeric antigen receptor (CAR), wherein the CAR construct preferably comprises a single chain variable fragment of an antibody (Fv) construct, a spacer region construct and a signaling region construct.
 7. The nucleic acid of claim 6, wherein the TCR construct comprises a TCR alpha chain construct and a TCR beta chain construct optimized for pairing with each other, wherein the TCR alpha and beta chains preferably each comprise (a) additional Cys residues relative to native human TCRs and/or (b) murine amino acid sequences in the constant regions, wherein otherwise, the TCR chains are of human origin.
 8. The nucleic acid of claim 4, wherein the transposon encodes at least two miRNAs, optionally, three, four, five, six, seven, eight, nine, ten or more miRNAs.
 9. The nucleic acid of claim 4, wherein miRNA encoded by the transposon is capable of silencing expression of a TCR alpha and/or TCR beta chain, wherein the miRNA is not capable of silencing expression of a TCR chain encoded by the transposon, wherein the transposon preferably encodes two miRNAs capable of silencing expression of a TCR alpha and TCR beta chain.
 10. The nucleic acid of claim 4, wherein miRNA encoded by the transposon is capable of silencing expression of a protein capable of limiting the therapeutic efficiency of the transferred cells, wherein the protein capable of limiting the therapeutic efficiency of T cells is selected from the group of inhibitory surface receptors comprising CTLA4, PDCD1, LAGS, HAVCR2 and TIGIT, from the group of intracellular proteins that negatively regulate TCR or costimulatory pathways comprising CBLB, CISH, DGK and TNFAIP3, from the group of intracellular proteins that limit cytokine production comprising SPRY2 and CREM or from the group of proteins stabilizing a dysfunctional T cell phenotype comprising MAF, EGR3, NDRG1 and DTX1.
 11. The nucleic acid of claim 4, wherein the transposon comprises a cargo nucleic acid flanked by a left and a right inverted repeat/direct repeat (IR/DR), wherein (i) the transposon is capable of being mobilized by a Sleeping Beauty transposase protein; (ii) the left IR/DR comprises an outer left DR motif and an inner left DR motif, wherein the outer left DR motif comprises the nucleotide sequence of SEQ ID NO:1 and the inner left DR motif comprises the nucleotide sequence of SEQ ID NO: 2; and (iii) the right IR/DR comprises an outer right DR motif and an inner right DR motif, wherein the outer right DR motif comprises an inverted sequence of the nucleotide sequence of SEQ ID NO:1 and the inner right DR motif comprises an inverted sequence of the nucleotide sequence of SEQ ID NO:
 2. 12. The kit of claim 1, wherein the minicircle DNA comprising said transposon is a nucleic acid comprising a transposon, wherein the transposon encodes a protein and a miRNA, wherein the nucleic acid encoding the protein comprises an intron comprising sequences encoding the miRNA, wherein expression of the protein and the miRNA is regulated by the same promoter, wherein the nucleic acid is selected from the group comprising a plasmid or minicircle DNA.
 13. A method for preparing transfected cells, comprising transfecting cells, preferably, electroporating cells, with the nucleic acids of the kit of claim 1, wherein said nucleic acid encoding the transposase is ivtRNA, wherein the cells which are electroporated preferably are primary cells and/or stem cells.
 14. The method of claim 13, wherein the cells which are transfected, preferably, electroporated, are primary T cells isolated from a patient, wherein the method optionally further comprises stimulating the T cells with one or more stimulants selected from the group comprising anti-CD3 antibodies, anti-CD28 antibodies, anti-CD137 antibodies, anti-CD134 antibodies, anti-CD357 antibodies, IL-2, IL-7, IL-15 and IL-21.
 15. A population of genetically modified cells comprising the nucleic acid of claim 4, wherein said population is preferably obtained by transfecting cells, preferably, electroporating cells, with the nucleic acids of the kit of claim 1, wherein said nucleic acid encoding the transposase is ivtRNA, wherein the cells which are electroporated preferably are primary cells and/or stem cells.
 16. A pharmaceutical composition comprising the population of genetically modified cells of claim 15, wherein, preferably, said cells are for use in treating a patient by adoptive T cell therapy, wherein the patient is selected from the group comprising cancer patients and/or patients infected with a viral or bacterial pathogen, and wherein the cells comprise T cells expressing a TCR construct. 